When performing a read or write operation on a disk drive, a variety of methods have been employed to reduce total data access time. One method, known as command queue reordering, reorders a command sequence that is received from a host computer into an execution sequence for a disk drive. Commands may be temporarily held in a command queue, where they may be reordered. Each command in the command queue contains an instruction for the disk drive that facilitates a read or write operation starting from a particular logical block address (LBA) on the disk. These commands may be uniquely identified by a label or tag, allowing them to be executed in a sequence different from that in which they arrive at the host computer. The idea behind reordering such commands is to minimize the path length that the read/write mechanical actuator or transducer must travel.
Another method to perform command queue reordering utilizes what is known as a rotational positioning optimization (RPO) algorithm. The RPO algorithm may utilize seek time and rotational latency when reordering the command queue. The total access time for a read or write command in the current command queue is computed with respect to the ending LBA of the last executed command, and the command having the shortest access time is moved to the front of the queue.
Yet another more advanced RPO algorithm may be used that considers the state of cache memory, in addition to the command queue. The more advanced RPO algorithm utilizes a cost function for not storing the block in the cache memory and an analogous cost function for storing the new data block into the cache memory. The above referenced RPO schemes try to optimize disk performance for queued commands, utilizing a host-centric approach.
Unfortunately, each of the previous schemes relies on a host-command oriented approach that employs a single work queue. This approach limits the effectiveness for tracking non-host-command work that occurs between the cache memory and the disk drive.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.